The exchange stiffness coefficient, A_ex, represents the strength of direct exchange interactions among neighboring spins. A_ex is linked to most of the magnetic properties such as skyrmion formation, magnetic vortex, magnetic domain wall width, and exchange length. Hence, the quantification of A_ex is essential to understanding fundamental magnetic properties, but little is known for the dynamics of A_ex on a sub-picosecond timescale. We report the ultrafast dynamcis of A_ex in an ordered magnetic state in Co/Pt ferromagnetic multilayer. Time-resolved magneto-optical Kerr effect and reflectivity measurements were analyzed for various pump fluences. We reveal that the significant dynamical reduction of A_ex is responsible for the dramatic increase of remagnetization time for high fluences. The analysis shows that A_ex dynamically varies, strongly affecting overall ultrafast demagnetization/remagnetization process. The investigation demonstrates the possibility of A_ex engineering in femtosecond timescale and thereby provides a way to design ultrafast spintronic devices.

交换刚度系数A _ex代表相邻自旋之间直接交换相互作用的强度。阿_前被连接到最磁特性如skyrmion形成，磁涡流，磁畴壁的宽度，和交换长度。因此，A _ex的量化对于理解基本磁性能至关重要，但是对于亚皮秒级的A _ex动力学知之甚少。我们报告了A _ex的超快动力在Co / Pt铁磁多层膜中呈有序磁态。针对各种泵注量，分析了时间分辨的磁光克尔效应和反射率测量结果。我们发现，A _ex的明显动态降低是高通量重磁时间急剧增加的原因。分析表明，A _ex动态变化，严重影响了整个超快退磁/复磁过程。该调查证明了飞秒级A _ex工程的可能性，从而提供了一种设计超快自旋电子器件的方法。